Lignin peroxidase catalyses the H2O2-induced oxidation of 4-methoxybenzyltrimethylsilane by an electron transfer mechanism. The intermediate radical cation undergoes preferentially C-alpha-H deprotonation to give 4-methoxybenzaldehyde whereas C-alpha-Si bond cleavage is a minor fragmentation pathway and leads to 4-methoxybenzyl alcohol. Similar results are obtained in the oxidation catalysed by the water soluble model compound 5,10,15,20-tetra(N-methyl-4-pyridyl)porphyrinatoiron(III) pentachloride. Instead, in the oxidation promoted by the genuine one-electron transfer oxidant potassium dodecatungstocobalt(III)ate C-alpha-Si bond cleavage is the exclusive fragmentation process of the intermediate radical cation. It is suggested that in the enzymatic and biomimetic oxidations of 4-methoxybenzyltrimethylsilane the deprotonation of the intermediate radical cation is promoted by the reduced form [PorFe(IV)=O] of the active oxidant, which is an iron-oxo porphyrin radical cation. (C) 2003 Elsevier Science (USA). All rights reserved.